1. Field of the Invention
This invention relates to controlling air/fuel ratio of an internal combustion engine having an electronic engine control system.
2. Prior Art
It is known to operate an internal combustion engine Using feedback controlled electronic engine control systems. A feedback signal can be provided by an exhaust gas oxygen sensor in the exhaust of the engine. The output signal from such exhaust gas oxygen sensor can indicate whether the engine is operating rich or lean of stoichiometry. This information is then processed by an electronic engine control module to adjust the air/fuel ratio by, for example, adjusting the amount of fuel injected into a cylinder. To ensure proper operation of such a feedback control system and confirm that the exhaust gas oxygen sensor is operating properly, it is known to test the exhaust gas oxygen sensor during system operation.
One such test can be to test the exhaust gas oxygen sensor response rate. For example, it is possible to drive the sensor at a fixed frequency using rich and lean air/fuel ratio excursions. That is, the output voltage of the exhaust gas oxygen sensor is monitored to determine how the sensor responds to known air/fuel ratio variations. Unwanted side effects of such a test are torque, engine speed, and engine load oscillations at the driven frequency. This invention overcomes .such undesired side effects.